A polycarbonate film for a battery separator and a method of manufacturing the same

Abstract

The application discloses a polycarbonate film for battery diaphragm, which comprises the following components in percentage by mass: polycarbonate resin 92-95%, polyacrylonitrile conductive particles 0.1-2%, flame retardant 0.4-2%, pigment filler 2-6%, antioxidant 0.05-0.1%, lubricant 0.1-0.4%, anti-dripping agent 0.1-0.5% and heat stabilizer 0.1-0.4%. The application further discloses a preparation method of the polycarbonate film for battery diaphragm. The addition of the polyacrylonitrile conductive particles can form an interpenetrating network structure in the polycarbonate film, so that the polycarbonate film has weak conductivity, the electrical property of the film is improved, the surface of the film has certain antistatic effect, the interpenetrating network formation can increase the toughness, impact resistance and tensile property of the film; in addition, the polyacrylonitrile material is non-combustible, and under the action of the flame retardant and the anti-dripping agent, the flame retardance of the polycarbonate film is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and more specifically to a polycarbonate film for battery separators and its preparation method. Background Technology

[0002] Polycarbonate film possesses excellent overall properties. Ordinary polycarbonate film is colorless and transparent with a light transmittance exceeding 90%. In addition to its superior electrical properties, the film also exhibits high tensile strength and rigidity, and its impact resistance is among the highest of thermoplastics. Polycarbonate film has low water absorption and molding shrinkage, and excellent creep resistance, resulting in dimensional stability of products under varying temperature and humidity conditions. This makes it suitable for manufacturing precision components, especially given its excellent cold and heat resistance, allowing for long-term operation within a wide temperature range of 100℃ to 130℃.

[0003] The separator is one of the key internal components in lithium-ion batteries. Its performance determines the battery's interface structure and internal resistance, directly affecting its capacity, cycle life, and safety performance. A high-performance separator plays a crucial role in improving the overall performance of the battery. The main function of the separator is to separate the positive and negative electrodes, preventing short circuits caused by contact between them. It also allows electrolyte ions to pass through. The separator material is non-conductive, and its physicochemical properties significantly influence battery performance. Different types of batteries use different separators. For lithium-ion batteries, since the electrolyte is an organic solvent system, separator materials resistant to organic solvents are required. Currently, polyolefin microporous membranes, such as polyethylene and polypropylene separators, are widely used in lithium-ion batteries. However, these separators have poor thermal stability, low wettability, low porosity, and low electrolyte absorption, posing safety risks and failing to meet current requirements.

[0004] To improve the performance of lithium-ion battery separators, researchers have made many improvements to the separator materials and components. For example, patent CN104868083B discloses a lithium-ion battery separator and its preparation method. This separator mainly includes 10-30 parts of PC, 4-10 parts of conductive carbon black, 0.1-1 parts of diphenyl sulfonate, 0.1-1 parts of sodium dihydrogen phosphate, 0.1-0.9 parts of other components, 0.1-0.7 parts of coupling agent, and 56.4-85.6 parts of diatomaceous earth. Although adding conductive carbon black to the polycarbonate system can increase the porosity of the battery separator and effectively prevent battery circuit failure, carbon black is a flammable substance. The addition of carbon black will greatly reduce the flame retardancy of the entire battery separator, thereby affecting the product's service life. Patent CN107887553B discloses a multifunctional lithium-sulfur battery separator and its preparation method, and specifically discloses a method for forming a functionalized coating on the surface of the PP separator. Since the functional coating is black, and as is well known, black easily absorbs light, when a black film is used as a lithium battery separator, heat is easily absorbed inside the battery. After prolonged use, the battery is prone to bulging, thus reducing the battery's lifespan. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects in the prior art and provide a polycarbonate for battery separators and a method for preparing the same, which aims to improve the mechanical and electrical properties of the battery separators while also giving them good flame retardancy.

[0006] To achieve the above objectives, the technical solution of the present invention is to provide a polycarbonate film for battery separators, comprising, by mass percentage, 92-95% polycarbonate resin, 0.1-2% polyacrylonitrile conductive particles, 0.4-2% flame retardant, 2-6% pigment filler, 0.05-0.1% antioxidant, 0.1-0.4% lubricant, 0.1-0.5% anti-drip agent, and 0.1-0.4% heat stabilizer.

[0007] To improve the performance of polycarbonate films as membranes and enhance their flame retardancy, this invention employs a technical solution involving the addition of polyacrylonitrile conductive particles, a flame retardant, and an anti-dripping agent to the polycarbonate system. The internal structure of the polyacrylonitrile conductive particles is a chain-like conductive structure, which reacts with polycarbonate resin under molten conditions to form an interpenetrating network, giving the polycarbonate a slight conductivity. This not only improves the electrical properties of the polycarbonate film but also provides a certain degree of antistatic effect on the film's surface. Furthermore, the formation of the interpenetrating network increases the film's toughness and impact resistance, significantly improving its tensile and other mechanical properties. In addition, polyacrylonitrile is a non-flammable material; with the help of the flame retardant and anti-dripping agent, the flame retardancy of the polycarbonate film is greatly enhanced.

[0008] In order to give the polycarbonate film excellent electrical properties and control its conductivity so that it can separate the positive and negative electrodes of the battery when used as a separator to prevent short circuit due to contact between the two electrodes, the mass fraction of polyacrylonitrile conductive particles added to the polycarbonate film of the present invention is controlled within 0.1% to 2%, preferably 0.5% to 1.5%, and further, the mass fraction of polyacrylonitrile conductive particles can be 0.5%, 0.8%, 1%, 1.2% or 1.4%.

[0009] A further preferred technical solution is that the polyacrylonitrile conductive particles are prepared by reacting a mixture of 5-12% by mass of elemental sulfur and 88-95% by mass of polyacrylonitrile particles at 300-800°C. Vulcanized polyacrylonitrile is often used as a positive electrode material in lithium batteries due to its excellent electrical properties. This is mainly because it contains CS bonds, which facilitate the free movement of electrons within the polycarbonate film, forming a conductive circuit, thereby giving the polymer matrix certain electrical properties.

[0010] A further preferred technical solution is that the flame retardant includes an organic sulfonate flame retardant or a siloxane flame retardant. The flame retardant preferably used in this invention is one of the above two, preferably a mixture of the two, wherein the organic sulfonate flame retardant is selected from potassium benzenesulfonylbenzenesulfonate (KSS), potassium perfluorobutyl sulfonate (PPFBS), and sodium 2,4,5-trichlorobenzenesulfonate (STB).

[0011] A further preferred technical solution is that, by mass percentage, the pigment filler comprises 0.1-0.2% phthalocyanine green, 0.5-0.6% titanium yellow, and 3-5% titanium dioxide. The pigment filler is added to give the polycarbonate film a certain color. The preferred color of the polycarbonate film in this invention is bluish-gray, that is, phthalocyanine green and titanium yellow are used to adjust the color of the polycarbonate film.

[0012] A further preferred technical solution is that the lubricant includes an internal lubricant and an external lubricant, wherein the mass fraction of the internal lubricant is 0.1-0.2%, and the mass fraction of the external lubricant is 0.1-0.2%. The internal lubricant primarily reduces friction within the polymer molecular chains during polymer processing. It exhibits good compatibility with the polymer, can be uniformly dispersed between molecular chains, improves polymer flowability, and enhances the surface finish of the product. When the external lubricant is added to polycarbonate to form a PC film, it often migrates to the surface of the polycarbonate film, forming a lubricant molecular layer at the interface, thereby improving the surface properties of the film. External lubricants are typically selected from high-grade fatty acids and organic wax products.

[0013] A further preferred technical solution is that the anti-dripping agent comprises pure PTFE powder or coated PTFE powder. The anti-dripping agent is a modified polytetrafluoroethylene powder, including both pure and coated types, commonly added to thermoplastics to increase melt strength and provide flame retardancy and anti-dripping properties. When the anti-dripping agent is added to polycarbonate resin, under the action of a screw, the high molecular weight polytetrafluoroethylene is fibrillated, forming a network structure to prevent the polycarbonate from melting and dripping, thereby improving the flame retardancy of the polycarbonate film.

[0014] This invention also discloses a method for preparing a polycarbonate film for battery separators, comprising the following steps:

[0015] (1) The pigment filler is mixed in a high-speed mixer, and the mixture is thoroughly and evenly mixed with polycarbonate resin, antioxidant and lubricant in a high-speed mixer and then fed into a twin-screw extruder for melt extrusion granulation to obtain the first polycarbonate granules.

[0016] (2) The conductive polyacrylonitrile particles, flame retardant, anti-dripping agent, heat stabilizer and polycarbonate resin are thoroughly and evenly mixed by a high-speed mixer and then fed into a twin-screw extruder for melt extrusion granulation to obtain the second polycarbonate granules.

[0017] (3) The first polycarbonate granules and the second polycarbonate granules are mixed in a high-speed mixer at a ratio of 1:1 to 3 to obtain polycarbonate flame retardant granules.

[0018] (4) The polycarbonate flame-retardant granules are put into a vacuum dryer for drying;

[0019] (5) The fully dried polycarbonate flame retardant granules are fed into an extruder, melted and extruded through a T-die, and the melt is calendered and shaped by a steel roller and a rubber roller, and then stretched into a polycarbonate film.

[0020] In preparing polycarbonate films, the technical solution adopted in this invention is to divide polycarbonate resin into two parts. Pigment fillers, antioxidants, and lubricants are added to one part to prepare a first polycarbonate resin. Polyacrylonitrile conductive particles, flame retardants, anti-dripping agents, and heat stabilizers are added to the second part to prepare a second polycarbonate resin. Finally, the two parts are mixed, and the polycarbonate film is prepared by extrusion and calendering. By dividing the polycarbonate resin into two parts and granulating them separately—one part for color adjustment and the other for polycarbonate modification—the first and second polycarbonate granules can be more fully mixed and cross-linked under the action of the screw. The polycarbonate film prepared by this method has more uniform color and superior, more stable performance.

[0021] The advantages and beneficial effects of this invention are as follows:

[0022] 1. The addition of polyacrylonitrile conductive particles can form an interpenetrating network structure inside the polycarbonate film, giving it weak conductivity. This not only improves the electrical properties of the film and provides a certain degree of antistatic effect on the surface, but the formation of the interpenetrating network can also increase the toughness, impact resistance, and tensile properties of the film. In addition, polyacrylonitrile is a non-flammable material, and with the help of flame retardants and anti-dripping agents, the flame retardancy of the polycarbonate film is greatly improved.

[0023] 2. By using a specific ratio of polycarbonate resin, polyacrylonitrile conductive particles, flame retardant, anti-dripping agent and other additives, the components work together to give the polycarbonate film excellent mechanical properties and flame retardant properties.

[0024] 3. When the vulcanized polyacrylonitrile conductive particles are added to the polycarbonate component, the melting reaction forms CS bonds inside, which helps electrons move freely inside the polycarbonate film, forming a conductive circuit, thereby giving the polymer matrix certain electrical properties.

[0025] 4. By dividing the polycarbonate resin into two parts and granulating them separately, one part is used for color adjustment and the other part is used for polycarbonate modification. The first and second polycarbonate granules can be more fully mixed and cross-linked under the action of the screw. The polycarbonate film prepared by this method has more uniform color and better and more stable performance. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1

[0028] A polycarbonate film for battery separators comprises, by weight percentage, 92% polycarbonate resin, 0.1% polyacrylonitrile conductive particles, 2% flame retardant, 0.1% phthalocyanine green, 0.5% titanium yellow, 4.8% titanium dioxide, 0.1% antioxidant, 0.1% internal lubricant, 0.1% paraffin wax, 0.1% anti-dripping agent, and 0.1% heat stabilizer. The polyacrylonitrile conductive particles are prepared by reacting a mixture of 5% sulfur and 95% polyacrylonitrile particles at 300°C. The flame retardant is potassium benzenesulfonylbenzenesulfonate, the internal lubricant is product D2000 from Dongguan Juona New Materials Co., Ltd., the anti-dripping agent is product SN3307PF from Guangzhou Shangneng Innovation Materials Co., Ltd., and the heat stabilizer is product B900 from BASF.

[0029] A method for preparing a polycarbonate film for battery separators includes the following steps:

[0030] (1) Phthalocyanine, titanium yellow and titanium dioxide are mixed in a high-speed mixer, and the mixture is then thoroughly and evenly mixed with polycarbonate resin, antioxidant and lubricant by a high-speed mixer and fed into a twin-screw extruder for melt extrusion granulation to obtain the first polycarbonate granules. The temperature during melt extrusion is 180℃.

[0031] (2) The conductive polyacrylonitrile particles, flame retardant, anti-dripping agent, heat stabilizer and polycarbonate resin are thoroughly and evenly mixed by a high-speed mixer and then fed into a twin-screw extruder for melt extrusion granulation to obtain the second polycarbonate granules. The temperature during melt extrusion is 180℃.

[0032] (3) The first polycarbonate granules and the second polycarbonate granules are mixed in a high-speed mixer at a ratio of 1:1 to 3 to obtain polycarbonate flame retardant granules.

[0033] (4) The polycarbonate flame-retardant granules are put into a vacuum dryer for drying;

[0034] (5) The fully dried polycarbonate flame retardant granules are fed into the extruder and melted and extruded through the T-die. The melting temperature is 200°C. The melt is calendered and shaped by one steel roller and one rubber roller and then stretched into a polycarbonate film.

[0035] Example 2

[0036] A polycarbonate film for battery separators comprises, by mass percentage, 93% polycarbonate resin, 2% polyacrylonitrile conductive particles, 0.4% flame retardant, 0.1% phthalocyanine green, 0.5% titanium yellow, 3.05% titanium dioxide, 0.05% antioxidant, 0.2% internal lubricant, 0.2% polyethylene wax, 0.3% anti-dripping agent, and 0.2% heat stabilizer. The polyacrylonitrile conductive particles are prepared by reacting a mixture of 10% by mass of elemental sulfur and 90% by mass of polyacrylonitrile particles at 500°C. The flame retardant includes 0.2% by weight of potassium benzenesulfonylbenzenesulfonate and 0.2% by weight of polysiloxane; the internal lubricant is product D2000 from Dongguan Juona New Materials Co., Ltd.; the anti-dripping agent is product SN3307PF from Guangzhou Entropy Energy Innovation Materials Co., Ltd.; and the heat stabilizer is product B900 from BASF.

[0037] A method for preparing a polycarbonate film for battery separators includes the following steps:

[0038] (1) Phthalocyanine, titanium yellow and titanium dioxide are mixed in a high-speed mixer, and the mixture is then thoroughly and evenly mixed with polycarbonate resin, antioxidant and lubricant by a high-speed mixer and fed into a twin-screw extruder for melt extrusion granulation to obtain the first polycarbonate granules. The temperature during melt extrusion is 200℃.

[0039] (2) The conductive polyacrylonitrile particles, flame retardant, anti-dripping agent, heat stabilizer and polycarbonate resin are thoroughly and evenly mixed by a high-speed mixer and then fed into a twin-screw extruder for melt extrusion granulation to obtain the second polycarbonate granules. The temperature during melt extrusion is 200℃.

[0040] (3) The first polycarbonate granules and the second polycarbonate granules are mixed in a high-speed mixer at a ratio of 1:1 to 3 to obtain polycarbonate flame retardant granules.

[0041] (4) The polycarbonate flame-retardant granules are put into a vacuum dryer for drying;

[0042] (5) The fully dried polycarbonate flame retardant granules are fed into the extruder and melted and extruded through the T-die. The melting temperature is 230°C. The melt is calendered and shaped by one steel roller and one rubber roller and then stretched into a polycarbonate film.

[0043] Example 3

[0044] A polycarbonate film for battery separators comprises, by weight percentage, 92% polycarbonate resin, 1% polyacrylonitrile conductive particles, 2% flame retardant, 0.2% phthalocyanine green, 0.6% titanium yellow, 3% titanium dioxide, 0.1% antioxidant, 0.1% internal lubricant, 0.1% polyethylene wax, 0.5% anti-dripping agent, and 0.4% heat stabilizer. The polyacrylonitrile conductive particles are prepared by reacting a mixture of 8% sulfur and 92% polyacrylonitrile particles at 800°C. The flame retardant comprises 1.2% potassium benzenesulfonylbenzenesulfonate and 0.8% polysiloxane. The internal lubricant is product D2000 from Dongguan Juona New Materials Co., Ltd., the anti-dripping agent is product SN3307PF from Guangzhou Entropy Energy Innovation Materials Co., Ltd., and the heat stabilizer is product B900 from BASF.

[0045] A method for preparing a polycarbonate film for battery separators includes the following steps:

[0046] (1) Phthalocyanine, titanium yellow and titanium dioxide are mixed in a high-speed mixer, and the mixture is then thoroughly and evenly mixed with polycarbonate resin, antioxidant and lubricant by a high-speed mixer and fed into a twin-screw extruder for melt extrusion granulation to obtain the first polycarbonate granules. The temperature during melt extrusion is 230℃.

[0047] (2) The conductive polyacrylonitrile particles, flame retardant, anti-dripping agent, heat stabilizer and polycarbonate resin are thoroughly and evenly mixed by a high-speed mixer and then fed into a twin-screw extruder for melt extrusion granulation to obtain the second polycarbonate granules. The temperature during melt extrusion is 230℃.

[0048] (3) The first polycarbonate granules and the second polycarbonate granules are mixed in a high-speed mixer at a ratio of 1:1 to 3 to obtain polycarbonate flame retardant granules.

[0049] (4) The polycarbonate flame-retardant granules are put into a vacuum dryer for drying;

[0050] (5) The fully dried polycarbonate flame retardant granules are fed into the extruder and melted and extruded through the T-die. The melting temperature is 280°C. The melt is calendered and shaped by one steel roller and one rubber roller and then stretched into a polycarbonate film.

[0051] Example 4

[0052] A polycarbonate film for battery separators comprises, by weight percentage, 95% polycarbonate resin, 0.5% polyacrylonitrile conductive particles, 0.4% flame retardant, 0.1% phthalocyanine green, 0.5% titanium yellow, 3% titanium dioxide, 0.1% antioxidant, 0.1% internal lubricant, 0.1% polyethylene wax, 0.1% anti-dripping agent, and 0.1% heat stabilizer. The polyacrylonitrile conductive particles are prepared by reacting a mixture of 12% sulfur and 88% polyacrylonitrile particles at 500°C. The flame retardant is polysiloxane, the internal lubricant is product D2000 from Dongguan Juona New Materials Co., Ltd., the anti-dripping agent is product SN3307PF from Guangzhou Entropy Energy Innovation Materials Co., Ltd., and the heat stabilizer is product B900 from BASF.

[0053] A method for preparing a polycarbonate film for battery separators includes the following steps:

[0054] (1) Phthalocyanine, titanium yellow and titanium dioxide are mixed in a high-speed mixer, and the mixture is then thoroughly and evenly mixed with polycarbonate resin, antioxidant and lubricant by a high-speed mixer and fed into a twin-screw extruder for melt extrusion granulation to obtain the first polycarbonate granules. The temperature during melt extrusion is 200℃.

[0055] (2) The conductive polyacrylonitrile particles, flame retardant, anti-dripping agent, heat stabilizer and polycarbonate resin are thoroughly and evenly mixed by a high-speed mixer and then fed into a twin-screw extruder for melt extrusion granulation to obtain the second polycarbonate granules. The temperature during melt extrusion is 200℃.

[0056] (3) The first polycarbonate granules and the second polycarbonate granules are mixed in a high-speed mixer at a ratio of 1:1 to 3 to obtain polycarbonate flame retardant granules.

[0057] (4) The polycarbonate flame-retardant granules are put into a vacuum dryer for drying;

[0058] (5) The fully dried polycarbonate flame retardant granules are fed into the extruder and melted and extruded through the T-die. The melting temperature is 230°C. The melt is calendered and shaped by one steel roller and one rubber roller and then stretched into a polycarbonate film.

[0059] Comparative Example

[0060] A polycarbonate film for battery separators comprises, by weight percentage, 95% polycarbonate resin, 4% titanium dioxide, 0.2% antioxidant, 0.2% internal lubricant, 0.2% polyethylene wax, and 0.4% heat stabilizer. The internal lubricant is selected from product D2000 of Dongguan Juona New Materials Co., Ltd., and the heat stabilizer is selected from product B900 of BASF.

[0061] A method for preparing a polycarbonate film for battery separators includes the following steps:

[0062] (1) Titanium dioxide, polycarbonate resin, antioxidant, lubricant and heat stabilizer are thoroughly and evenly mixed by a high-speed mixer and then fed into a twin-screw extruder for melt extrusion granulation to obtain polycarbonate granules. The temperature during melt extrusion is 200℃.

[0063] (2) The polycarbonate granules are put into a vacuum dryer for drying;

[0064] (3) The fully dried polycarbonate granules are fed into the extruder and melted and extruded through the T-die. The melting temperature is 230°C. The melt is calendered and shaped by one steel roller and one rubber roller and then stretched into a polycarbonate film.

[0065] (4) Print a bluish-gray ink on one side of the polycarbonate film obtained in step (3) and dry it.

[0066] The polycarbonate films prepared in Examples 1-4 and the comparative example were tested for tensile strength and tensile stress according to standard ISO 527-1-2012, impact performance according to standard ISO 179-1-2010, and flame retardancy according to UL 94. The colorimetric values ​​were measured using a colorimeter, and the color difference value ΔE was recorded. The test data are shown in the table below.

[0067] Example Tensile strength (MPa) Tensile stress (MPa) <![CDATA[Impact strength (kJ / m 2 )]]> Flame retardancy Color difference (ΔE) 1 2108 60 55 V0 0.23 2 2417 68 61 V0 021 3 2450 66 62 V0 0.21 4 2325 61 57 V0 0.18 Comparative Example 2050 58 48 V1 2.15

[0068] As can be seen from the data in the table, the polycarbonate film of the present invention has excellent tensile and impact resistance properties, flame retardancy can reach V0 level, and the products made from it have no color difference.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polycarbonate film for battery separators, characterized by, By mass percentage, its components include: Polycarbonate resin 92~95%; Polyacrylonitrile conductive particles 0.1~2%, which are prepared by reacting a mixture of elemental sulfur with a mass fraction of 5~12% and polyacrylonitrile particles with a mass fraction of 88~95% at 300~800℃; Silicone flame retardant 0.4~2%; Pigment filler 2~6%, which includes phthalocyanine green 0.1~0.2%, titanium yellow 0.5~0.6%, and titanium dioxide 3~5%; Antioxidant 0.05~0.1%; Lubricant 0.1~0.4%, which includes internal lubricant and external lubricant, the mass fraction of the internal lubricant being 0.1~0.2% and the mass fraction of the external lubricant being 0.1~0.2%; Anti-dripping agent 0.1~0.5%, which is a coated PTFE powder; Thermal stabilizer 0.1~0.4%.

2. A method of producing the polycarbonate film according to claim 1, characterized by, The method includes the following steps: (1) Mix the pigment filler in a high-speed mixer, and then mix the mixture with the polycarbonate resin, antioxidant, and lubricant in a high-speed mixer to obtain a first polycarbonate granule; (2) Mix the polyacrylonitrile conductive particles, silicone flame retardant, coated PTFE powder, and thermal stabilizer with the polycarbonate resin in a high-speed mixer to obtain a second polycarbonate granule; (3) Mix the first polycarbonate granule and the second polycarbonate granule in a high-speed mixer at a ratio of 1:1~3 to obtain a polycarbonate flame-retardant granule; (4) Dry the polycarbonate flame-retardant granule in a vacuum dryer; (5) Introduce the fully dried polycarbonate flame-retardant granule into an extruder, melt extrude it through a T-shaped die, and then draw a polycarbonate film by calendering and shaping the melt with a steel roller on one side and a rubber roller on the other side.